On-board water treatment and management process and apparatus

ABSTRACT

A contactor apparatus is provided to treat ballast water that has exited a ballast tank before being expelled from a water-borne ship. Within the contactor apparatus, means are provided for supplying a combination of acoustic energy and dissolved ozone. The acoustic energy can be provided at two or more frequencies (e.g., at 16 and 20 kHz). The acoustic energy and dissolved ozone, together, offer a more-effective and more-efficient mode of disinfecting the ballast water before release.

GOVERNMENT SUPPORT

The invention was supported, in whole or in part, by Grants No.NA96RG0478, No. NA03OAR4170008 and No. NA04ARA4170150, from the NationalOceanic and Atmospheric Administration. The U.S. Government has certainrights in the invention.

BACKGROUND

It is estimated that as many as 3,000 alien species per day aretransported throughout the world in the holds of ships. Most of theseorganisms do not survive the stress of the voyage and are not capable ofcompeting in their new environments when they are discharged in a remoteport. However, the records are replete with thousands of examples wherealien species have thrived in their new environments and gone on towreak ecological and economic havoc in their new surroundings. The mostcelebrated example of recent times is the zebra mussel (Dreisennapolymorpha) infestation of the Great Lakes and the Mississippi andHudson Rivers. The infestation was established in the middle of the lastdecade and their numbers have exploded because of their efficientreproduction. The zebra mussels cling tenaciously to surfaces such aswater and drain pipes and soon cause flow problems in water treatmentplants and cooling towers. The infestations are expected to cost $5billion in control efforts. Another rapidly spreading exotic specie inthe Great Lakes ecosystem is the Eurasian ruffe, a foraging fish relatedto North American perch. Native fish populations are seriously affectedby the feeding and reproduction capacity of the ruffe. Countlessexamples of alien or exotic species becoming established exist in otherareas of the world, as well.

Regulation of ballast water management and treatment will be required tolessen the probability of alien species introduction and the concomitanteconomic and environmental impacts. The currently favored approach tomitigating the threat from ballast water is to exchange the water in theopen ocean during transit. This practice can lower the density of largerorganisms in the water from 170 to 2 per metric ton. Severalshortcomings of the procedure exist, however. Safety of the ship iscompromised when ballast is exchanged in open waters. Care must beexercised to avoid adversely affecting the performance of the ship inhigh seas and to avoid causing mechanical failure due to unsymmetricalloading of the ship. Thus, some ships are hesitant to adopt thepractice. Even ships willing to comply with the practice can only manageto do so about 40% of the time. Also, a fraction of the ballast water isnot pumpable and remains in the compartment along with sediments.Organisms may establish permanent or semi-permanent communities in thisenvironment and serve as a reservoir of infestation to freshly loadedballast. It is recognized that ballast exchange is neither practical noreffective as a means of treating ballast water, and that either land- orwater-based treatment facilities are needed to effectively deal with theproblem.

Most ships have a ballast water capacity that is 25 to 30 percent oftheir dead weight tonnage, with 25 percent being the norm. The volume oftotal ballast can range from 13,500 to 9.3 million gallons. An averageballasting rate is on the order of 300,000 gallons per hour, while anaverage deballasting rate is around 1 million gallons per hour for aslong as 10 hours. Pumping and treating capacity of up to 10 milliongallons per ship deballasting may ultimately be required of a treatmentfacility located dockside at the port. Dockside facilities would requirespace for constructing a treatment plant that could handle flows of thatmagnitude and the infrastructure and capacity to service all shipsunloading in port.

On board treatment systems are increasingly considered to be a viablealternative. By taking on clean water, the transport of organisms iseliminated. Filtration of incoming ballast at the 251 μm size range hasbeen determined to be an effective method of reducing the loading ofzooplankton and phytoplankton in incoming ballast. Backflush water issimply discharged back into the harbor of origin. Secondary treatmentoptions, such as ozone or UV, could be coupled with filtration fordeactivation of smaller organisms. Treatment could also be carried outwhile the ship was under way, but the transit time may not be adequate.Shipboard treatment is hindered by the lack of space for installing theappropriate equipment, and sometimes by the lack of a suitable powersource for pumping ballast water for treating. Treatment duringdeballasting may require a larger capacity system, and substances fromthe hold or ballast tanks, such as iron or sediment, can interfere withthe treatment.

Ballast water presents unique challenges to conventional disinfectiontechnologies owing to the large number of organisms, the diversity oftheir composition, and the chemical and physical characteristics ofballast water. Some characteristics of conventional technologies thathave been applied to ballast water treatment are outlined, below.

Filtration:

Microfiltration removes most unwanted organisms; though, it may be toocostly for large ships. The backflushing rate is excessive at 25 μm. 50μm particle size removal is achievable, but 100 μm may be the practicallimit. Microorganisms and dinoflagellates pass. Most likely, filtrationis used in combination with UV or chemical biocides.

Thermal:

The water is heated to 60° C. for pasturization, which requires about 90MW of energy on average ship. However, often only 20 MW is available.Moreover, thermal treatment generally is not practical in northernclimates.

UV Irradiation:

Ultraviolet (UV) irradiation can be effective if water is not turbid.Only a short contact time is required, and the equipment can be had fora small capital expenditure. A portable unit may be immersed in ballasttanks for treatment during transit. There are no hazardous reagents usednor byproducts produced. UV irradiation requires filtration or cyclonepre-treatment to maintain low turbidity. UV irradiation is not effectiveagainst higher organisms or cysts.

Chlorine:

Chlorine is effective at high doses and long contact times. However,chlorine is corrosive and hazardous to store and handle. Chlorine alsoproduces chlorinated hydrocarbon byproducts. Though chlorine treatmentis relatively inexpensive, the gas is potentially lethal.

Ozone:

Ozone can be effective at low doses and short contact times; ozonedemand increases the necessary dosage. In previous methods, ozone wasapplied within the ballast tanks, where the effectiveness of ozone canbe reduced by organic matter from sediment, and the effectiveness of theozone was compromised in that ozone does not readily penetrate/diffusethrough the sediment in the ballast, which is where many organismsreside. Bromine reactions and formation of halohydrocarbons were also amajor concern. Further still, ozone treatment systems tend to beexpensive, with a large initial capital investment. Ozone gas is alsotoxic; accordingly, monitoring equipment is employed while the system isoperating. Ozone gas also has a corrosive effect on the ballast tankwhen employed in the tank. Nevertheless, ozone kills even highlyresistant forms such as spores and cysts. Moreover, no hazardous reagentstorage is needed, as ozone can be generated from dry air on demand.

Ozone is a mature technology, having been in use for over a century as awater and waste water treatment technology. The contact dosage needed tokill invertebrates in typical applications is on the order of 0.3 mg/L;and the most-resistant organisms, such as Cryptosporidium oocysts, canbe killed via exposure to an ozone concentration of about 1.5 mg/L for 1minute. Ozonation can be used to disinfect microorganisms, oxidize Fe²⁺and Mn²⁺, control taste and odor, enhance coagulation-flocculation andremove color. An allotrope of oxygen, ozone is a highly reactive gaswith a pungent odor having a standard oxidation-reduction potential of2.08 volts. Because of this reactivity, the chemistry of the water willhave an effect on the amount of ozone required for inactivation oforganisms. Ozone readily attacks natural organic matter present in thewater. At high pH (e.g., about 12), ozone may decompose to form theextremely reactive hydroxyl radical, which readily reacts with thecarbonate or bicarbonate in waters. In ocean brines, ozone reacts withbromide to form brominated organic compounds, as well as bromate. Also,lower valent transition metals such as Fe²⁺ and Mn²⁺ will consume ozone.

Oemke and van Leeuwen (in “Chemical and Physical Characteristics ofBallast Water: Implications for Treatment Processes and SamplingMethods,” CRC Reef Research Centre, Technical Report No. 23, 1998, andin “Potential of Ozone for Ballast Water Treatment,” CRC Reef ResearchCentre, March 1998) have identified several potential problems whenozonating marine ballast waters, the most serious of which is reactionwith bromide. The bromide concentration in seawater is 1.915 mg/L per %salinity. They estimated a significantly high bromide concentration of40 mg/L in ballast water sampled during their work. The reactionchemistry of ozone with bromide is complex, and involves a cyclicdecomposition reaction with bromide that simply consumes ozone andregenerates bromide. The reaction is mediated by the hypobromite ion.This anion undergoes an additional reaction with ozone to form bromate.In this reaction, one mole of hypobromite consumes two moles of ozone.Hypobromous acid is a weak acid with a pKa of 8.8 at 20° C. Theconjugate acid of hypobromite does not further react with ozone, so theauthors suggest that lowering the pH to about 7 would assist inquenching the cyclic decomposition and the formation of bromate. Thebromide reaction is further complicated in the presence of dissolvedorganic matter. The reaction paths become so complex that empiricalmodels are required to predict the amount of bromate that forms.Organobromine compounds form, as well, a concern from a health andenvironmental standpoint.

The concept of shipboard treatment of ballast water presents a number ofchallenges that any technological solution would typically need toaddress. These challenges include a variety of constraints andperformance expectations. First, large volumes (up to 10 milliongallons), which are routinely taken on and discharged as part of thenormal ballast operation of the ship, must be treated at a rate highenough to keep up with the ship schedule. Second, both macroscopicorganisms and microorganisms and their spore and cyst forms must bekilled or inactivated. Third, the quality of ballast water typically ispoor, with high turbidity and a difficult chemical matrix. Fourth, bothspace and power are limited aboard a typical ship.

SUMMARY

The National Research Council's Committee on Ships' Ballast Operationshas negatively rated ozone for the reasons cited above, as well as forthe maintenance requirements of the generators and corrosion problemsinduced by the ozone. One can limit the side reactions of ozone byreducing the amount of ozone dosing and increasing the contact time. Atleast part of the killing power of ozone resides in merely contactingthe organisms with ozone bubbles. In a limited space environment, suchas the pump or engine room of a ship, it may not be possible withprevious technology to provide the time-space capacity necessary tosignificantly lower the ozone dose and improve its effectiveness as abiocide. In accordance with the methods described below, an acousticmixer (such as those available from Advanced Sonics, Oxford, Conn.) usedin combination with an ozone generator can provide improved contactingand intense acoustic fields.

Despite the complexities and myriad chemical reactions that ozone canundergo, it remains a powerful and practical treatment strategy. One canmonitor retention time and residual ozone concentration to determine ifthe system is functioning correctly. Thus control algorithms can useinput data from a flow meter and an ozone concentration monitor at thedischarge of a contact chamber to insure that the treatment is adequate.This ease of monitoring is a distinct advantage over other treatmentoptions, such as UV. Even slight decreases in radiation intensities canaffect the killing efficiency. If organisms are not fully killed, theymay repair their DNA with dark repair enzymes and recover. Further,there may be concern about radiation-induced mutations in survivingorganisms.

The water treatment apparatus described herein can be implemented on awater-borne ship. The apparatus is coupled with a conduit for deliveringwater from the sea to the ballast tanks or, more preferably, with aconduit for delivering ballast water from the ballast tanks back to thesea in the barge or ship. Accordingly, the water is treated outside theballast tanks, before the water enters or after it leaves a ballasttank. The apparatus combines the following three systems in itstreatment of the water: a sonic reactor for delivering sonic wavesthrough the water, a regulated ozone source for delivering ozone intothe water, and a filter for filtering the water before it is subjectedto the dissolved ozone treatment. The apparatus can disinfect waterflowing through the conduit into or out of the ballasts of a ship at acontinuous flow rate of 150 gallons or more per minute.

Ozone can be an effective killing technology against undesirableorganisms transported in ballast water if it is coupled with a sonicreactor that radiates high-intensity energy and filtration. This form ofenergy enables mass transport and micromixing that cause improved ozoneutilization. Filtration, which can be provided via a filter positionedupstream from the ozone source and sonic reactor, reduces the amount ofmaterial to be treated. A premise of methods and apparatus describedherein is that contacting the organisms in the ballast water with theozone in a sonic reactor can significantly lower the dose of ozonerequired to kill organisms. The lowered ozone requirement can result inless byproduct formation and improved economics.

The acoustic mixer uses a mechanically driven acoustic transducerpromote intimate mixing of gases, liquids, and solids for chemicalprocessing. Two or more resonating members or piezoelectric ormagnetostrictive transducers operating at different frequencies (e.g.,at 16 and 20 kHz) can be employed in the mixer to generate the acousticvibrations. The same fluid dynamic mechanisms responsible for theenhanced contact in chemical systems will improve the contact betweenthe organisms in ballast water and the ozone bubbles, resulting ingreater mortality at small dosing rates. The high intensity acousticpressure wave that is propagated in the reactor will stress andtraumatize the organisms, increasing their vulnerability to the ozone.

Advantages of the apparatus and method include the following: (a) theapparatus can be compact (i.e., having a small footprint that can fitwithin available space aboard a ship); (b) the apparatus and methods canbe effective in inactivating organisms with a short contact/exposuretime; (c) there is no need for storage or handling of toxic chemicals;(d) there are no residual concentrations of environmentally harmfulsubstances; (e) the methods and apparatus allow ballast water, to betreated as part of normal ballasting or deballasting operations at aflow rate that is compatible with the operational schedule of the ship;and (f) the treatment can be performed outside the ballast tanks, wherethe sediment in the tanks will not compromise the disinfection. Further,the apparatus and methods are economically attractive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an asymmetric collapse of a cavitationbubble.

FIG. 2 is a schematic representation of the principle of operation ofthe acoustic mixer.

FIG. 3 is a chart showing the oscilloscope traces of hydrophone signalsin a sonic reactor; the intensities correspond to 215 dB in the topsignal and 209 dB in the bottom signal.

FIG. 4 is a chart illustrating the gas-liquid relationships for ozone inan acoustic pressure field.

FIG. 5 is a chart illustrating the gas-liquid relationships for ozone inan acoustic pressure field with coupled reaction in solution.

FIG. 6 is a process diagram of the sonic-ozone treatment.

FIG. 7 is an illustration of a ballast water treatment system configuredin a standard 8-foot-by-8-foot shipping container.

FIG. 8 is a plot of viable B. subtilis CFU in a sonicated reactor at twointensities.

FIG. 9 is a chart showing the trace of a 1.5 mg/L experiment involvingdiffuser dispersal in deionized water.

FIG. 10 charts the exposure curves for the diffuser.

FIG. 11 charts a high-intensity acoustic signal in a matrix of water andozone-containing gas bubbles.

FIG. 12 plots exposure curves for 205 dB experiments in deionized water.

FIG. 13 plots exposure curves for 215 dB experiments in deionized water.

FIG. 14 charts the decrease in endospore viability in synthetic seawaterat a pH of 7.5.

FIG. 15 charts the decrease in endospore viability under the sameconditions, except at a pH of 9.2 in synthetic seawater.

FIG. 16 charts the trace of dissolved ozone concentration duringozonation with 440 watts of power and 0.8 m³ hr⁻¹ of ozone.

FIG. 17 charts the reduction in endospore viability with ozone poweroutput in an actual ballast water challenge.

DETAILED DESCRIPTION

The technology is based on generating acoustic vibrations in processfluids to perform useful work such as mixing and interphasal masstransport. The acoustic frequency can be low or high, though frequenciesin the audible range can produce excessive noise and resultantdiscomfort for those on board the ship. Frequencies at the lower end ofthe ultrasonic range (e.g., between 16 and 20 kHz) can be highlyeffective; and the use of dual frequencies (the simultaneous applicationof two frequencies) can further improve effectiveness. When theresultant vibrations agitate a fluid under conditions such that thefluid can absorb the vibrational energy, phenomena occur that enhancemixing and mass transport.

Description of Sonic Technology:

Approach:

The fundamental processes that the sonic technology of all frequencyregimes exploit are cavitation and acoustic streaming.

Cavitation:

Tensile forces can be imposed in a liquid via the transmission ofacoustic rarefaction waves, which can overexpand the liquid. If theliquid is sufficiently expanded by these tensile forces, vapor cavitiesare formed. The formation of these cavities is the onset of cavitation.Cavitation in liquids is the nucleation, growth and subsequent collapseof bubbles. During collapse, high pressures, high temperatures and largeshear forces can result. Their magnitude is a function of intensity andnature of the driving force (frequency and power) that are imposed inthe fluid. The magnitude of these effects is a function of the liquidviscosity, liquid surface tension, liquid temperature, vapor pressure,particulate content and dissolved or entrained gases.

The use of cavitation in chemical processing is referred to assonochemistry. Typically, frequencies in what is known as the power bandof ultrasound ranging from 20 kHz to 900 kHz are employed in existingsonochemistry applications. Temperatures of 5,000° C. and pressures ofseveral hundred atmospheres have been measured in bubbles formed duringcavitation. Although these conditions exist for only microseconds, thetemperatures and pressures, coupled with the mixing that occurs in thecavitating media, are extremely effective in accelerating chemicalreactions far beyond rates that are feasible via normal processingsystems. Moreover, during the cavitation-induced asymmetric collapse ofthese energetic bubbles 12, liquid micro-jets 14 are generated, whichimpinge on surfaces 16 with great force, as illustrated in FIG. 1. Thesehigh-velocity jets 14 produce extraordinarily large local shear forces.The conditions created by cavitation are extremely inhospitable fororganisms.

Acoustic Streaming:

Acoustic streaming is a time-independent circulation of fluid induced bya sonic field. Acoustic streaming is caused by momentum dissipation inthe fluid by the absorption and propagation of sound. This transfer ofacoustic radiation is proportional to the acoustic intensity and can bequite profound in violently disturbing the fluid. Acoustic streaming hasbeen demonstrated to be responsible for enhanced heat transfer rates,improved mass transfer, changes in reaction rates, emulsification anddepolymerization.

The phenomenon is of particular interest in this application of thetechnology because of its ability to cause large velocity gradients andshearing stresses, both of which accelerate and promote particlecollisions, thereby virtually eliminating concentration gradients, andthus accelerating and enhancing mass transport processes. Smallorganisms and cysts disaggregate from other suspended particles. Somedegree of physical damage or destruction results from the greatlyaggravated hydraulic action, and the mass transport of ozone to the cystsurfaces is enhanced.

The combined effects of the cavitation bubbles (high pressures andtemperatures), jetting of fluids, strong-acoustic streaming and thefluctuating, high-energy acoustic sound field induced into the fluid bythe acoustic mixing process that permeates the liquid, virtuallyprovides an “acoustic minefield,” which will cause stress, degradationand, very likely, destruction of organisms. At a minimum, thisacoustically driven hydraulic activity will greatly assist theeffectiveness of ozone in killing organisms in ballast water.

Sonic Frequencies:

Acoustic energy applications in the field of sonochemistry havegenerally been conducted, e.g., at 20 kHz and higher. Even though theuse of high-frequency acoustics to accelerate chemical reactions is wellestablished, they have generally only been demonstrated in bench scaleexperiments. Consequently, the use of ultrasonics has not beenintegrated into many industrial chemical processes. The fundamentallimitation for large-scale ultrasonics applications is illustrated inEquation 1, which is derived from first principles. This clearly showsthat the attenuation of sonic energy, a, in liquid media is proportionalto the square of the frequency, f.

$\begin{matrix}{{a = {\frac{2\pi^{2}f^{2}}{{pc}^{3}}\left( {{\frac{4}{3}n_{s}} + n_{B} + \frac{\left( {\gamma - 1} \right)K}{C_{P}}} \right)}},} & (1)\end{matrix}$where ρ is density, c is the speed of sound, n_(s) is shear viscosity,n_(B) is bulk viscosity, γ is the specific heat ratio, C_(p) is thespecific heat, and K is the thermal conductivity of the medium.

Using Equation 1, it can be shown that large amounts of energy arerequired to generate cavitation phenomena to propagate distances ofpractical interest into media for industrial scale systems at higherultrasonic frequencies, e.g., generally 20 kHz to 500 kHz. These factorshave precluded the application of sonochemical devices for industrialprocessing applications. Because of the potential for significantimprovements in process enhancement achievable by cavitation, attemptsare underway to circumvent the scaling issues by various techniques.However, practical means to scale up ultrasonic driven systems have notbeen established, nor is a commercial process for doing so apparent.

Higher-intensity cavitation generates higher temperatures, pressures andshear forces; these are the mechanisms responsible for the sonochemicaland mechanical acceleration of kinetic processes in liquids andslurries. As shown in Equation 2, one can establish a relation betweenintensity, I, of acoustic energy in media, physical properties (density,ρ, and velocity of sound, c), frequency of vibration, ƒ, and vibrationalamplitude, A.

$\begin{matrix}{I = {\frac{1}{2}\rho\;{cf}^{2}{A^{2}.}}} & (2)\end{matrix}$From Equation 2, it can be seen that the acoustic intensity can beenhanced either by increasing the frequency or by increasing theamplitude of the driving force.Acoustic-Mixing Process and Machine:

“Acoustic mixer” is a term used to describe a broad-based machine thatcauses acoustic oscillations. As previously noted, such a mixer can beobtained from Advanced Sonics. The acoustic mixer has been demonstratedto generate strong-cavitation in liquids and slurries. The principle ofoperation utilizes the transmission of the sonic energy into fluid mediato cause a “catalytic-like” effect to accelerate or enhance chemicalreactions and other processes.

FIG. 2 is a schematic depicting the underlying principle of operationsfor an embodiment of an acoustic-mixing machine. The mechanical energyfrom an electrical or hydraulic motor 16 is used to rotate an eccentricdrive assembly that is coupled to a mechanical member 18, e.g., one ormore bars or plates. The most common members 18 are a specially treatedsolid steel bar and a hollow tube resonator (HTR). The rotationalfrequency of the oscillator 20 is adjusted to bring this mechanicalmember 18 into resonance. The concept of resonance is important tostress here, because, like its electrical circuit analog, a tunedmechanical resonant oscillator 20 is capable of delivering orders ofmagnitude more vibrational energy 22 to the load when operated at itsfundamental resonant frequency or one of its harmonic overtones. Whenthis resonant member 18 is vibrated in a liquid or slurry media,cavitation results from the intensity of the energy transmitted.

In this embodiment, the fundamental frequency of the resonant bars isnominally 75 Hz, as seen in FIG. 3, which is an oscilloscope trace ofthe signal from a hydrophone immersed in water while the sonic bar isvibrated. Conditions in the reactor were changed to produce the moreintense wave at the top. The hydrophone is a calibrated transducer formeasuring the intensity of acoustic waves. The intensity of the topsignal corresponds to a 215 dB re 1 μPa sound pressure level.

The phenomena associated with the acoustic field would also make thecontactor suitable as a UV reactor by inducing turbulence at the lampsurface, keeping the lenses clean and providing a high throughput oforganisms. The test reactor used for batch tests is fabricated from 316stainless steel and can be configured for batch processing of 10 to 35 Lquantities, or as a flow-through reactor. One embodiment of a continuouscontactor is substantially in the form of a cylinder having a diameterof about 0.6 m and a height of about 2.4 m and can be incorporated inthe shipboard skid. The axis of the cylinder can be oriented verticallyor horizontally on board the ship.

Observations made during the reactor operation in the Montec laboratoryclearly indicate that the technology promotes very energetic andturbulent solid/liquid and solid/gaseous mixing, sufficient to enhancegas solvation and mixing. The sonics process produces acoustic streamingin a fluid by adsorption of sound in the fluid and collapsing bubbles.

Dynamics of Ozone Solubility in an Acoustic Pressure Field:

In one embodiment, a bubble of ozone-enriched oxygen exposed to anacoustic pressure field experiences a contraction due to the pressurepart of the wave lasting 666 msecs. At an intensity of 215 dBA, the RMSaverage pressure during this period is 0.8 atmospheres.

The bubble dynamics cause two effects:

-   -   The boundary layer around the bubbles is in shear due to the        rapid expansion and contraction, thus gradients do not become        steep; and    -   The increased pressure of gas in the bubble on the contraction        side increases the solubility of the ozone for about 6 msec per        vibration cycle.

The solubility of ozone in a liquid is given by Henry's Law as:P_(O3)=H[O₃]_(sat)  (3)where P_(O3) is the partial pressure of ozone in the bubble, H isHenry's Law constant for ozone (which is a function of temperature), pH,and ionic strength of dissolved solutes in water. Inside the gas bubblethe total gas pressure P_(g) is:P _(g) =P _(h) +P _(a)  (4),where P_(h) is the hydrostatic pressure, and P_(a) is the acousticpressure. The gas inside the bubble is composed of oxygen and ozone:P _(g) =P _(O2) +P _(O3)  (5).

The partial pressure of ozone in the bubble would be given by:P_(O3)=X_(O3)P_(g)  (6),where X_(O3) is the mole fraction of ozone in the bubble. For a gasstream that is 2% by weight ozone, the mole fraction is about 0.014.

The rate of ozone mass transfer into the liquid phase is given as:D[O₃ ]dt=k _(L) a([O₃]_(sat)−[O₃])  (7),where [O₃] is the bulk solution concentration of ozone at any time and[O₃]_(sat) is the saturation concentration for ozone given by Equation3. k_(L) is the liquid mass transfer coefficient of the gas and “a” isthe specific gas liquid interfacial area. In the liquid film surroundingthe bubble, ozone will start to diffuse across the interface. Theprocess can be visualized for purely physical absorption as in FIG. 4(where spatial coordinates are represented on the horizontal axis, andpressure is represented on the vertical axis). As shown in FIG. 4, ozonein the gas phase with partial pressure, P_(O3), diffuses across a filmof liquid at the gas liquid interface, and the aqueous ozoneconcentration [O₃] rises until [O₃]_(sat), the equilibrium concentrationfor the partial pressure and temperature, is reached. The driving forcefor the dissolution of ozone is the “ozone deficiency,” i.e., the widthof the gap between [O₃]_(sat), and [O₃]. The ozone deficit is indicatedby the two arrows. Implicit in the representation is the fact that anincrease in P_(O3) will result in a higher [O₃]_(sat) and an increase inthe width of the gap.

When the rarefaction part of the wave acts on the bubble, P_(O) ₃ willdecrease as the volume of the bubble increases. The aqueousconcentration of ozone will now be out of equilibrium with the lowerpartial pressure of ozone in the bubble and start to diffuse back intothe bubble. If the acoustic pressure variation were symmetric about therelative pressure=0 axis, and if the rates of ozone diffusion in bothdirections were the same, one would expect that no net gain in ozonesolubility would be obtained under sonication.

Ozone absorption coupled with chemical reaction results in a differentconcentration profile. FIG. 5 is a plot of ozone concentration profilewhen either a fast or slow chemical reaction consumes the ozone in theliquid. If conditions in solution are such that direct reaction of ozonewith some substrate or decomposition of ozone to form hydroxyl radicalsis occurring, the concentration of ozone can range from zero to somevalue less than [O₃]_(sat), depending on the rate of the reaction. Thisis in spite of the fact that ozone is being transferred from the gas tothe liquid phase. The persistent width of the deficiency gap gives riseto a “chemically enhanced” rate of uptake of ozone.

This maintenance of an ozone deficit through the presence of anoxidizable substrate contributes to the mass transfer efficiency.Because of its ability to “pump” ozone into a liquid, the rate of masstransfer is greatly enhanced when the concentration of ozone hovers nearzero in solution because of its rapid consumption by an oxidizablesubstrate or its decomposition to hydroxyl radical. Some or all of theozone pumped in during the compression wave is consumed by chemicalreaction before the rarefaction part of the wave lowers the partialpressure of ozone in the bubble, resulting in a lower solubility ofozone.

Coupling of Ozone Disinfection with Sonic Energy for On-Board BallastWater Treatment:

Benefits of incorporating an acoustic mixer (also referred to herein asa “contactor” or “reactor”) in an onboard ballast water treatmenttechnology include:

-   -   Promotion of better contact of ozone with target organisms, thus        reducing the physical “time-space” requirement and permitting        its use aboard ships;    -   Traumatization of organisms through the imposition of a strong        (215 dB re 1 μPa) acoustic field which may synergistically        contribute to the inactivation of the organism; and    -   Reduction of the amount of ozone, which must be used to effect        inactivation, thus minimizing the negative influence of bromide        in marine waters and improving the economics.

One mechanism that results in higher disinfectant dosage requirements isthe association of viable particles with suspended matter in the water.Sonic disruption of these aggregates would enhance the contact of ozonewith the target organisms. Also, organisms in a weakened physical stateare more susceptible to inactivation. It is known that Cryptosporidiumoocysts shaken with sand and then exposed to chlorine for 5 minutesexperience a significant decrease of vitality. Normally, over 90 minutesof contact time are required at 80 μg/L chlorine dosage to achieve thesame level of disinfection. Administration of ultrasound and ozonetogether produces an enhanced rate of Giardia cyst destruction,presumably through cyst damage and enhanced mass transport of ozone intosolution.

Ultrasonic energy has routinely been used in laboratories to disruptcells. Typically, a frequency of 20 kHz and an energy intensity of 10W/cm² are required for cell rupture when sonication is used alone.Technology based on ultrasound alone as a disinfection mechanism hasrecently been proposed for Cryptosporidium in drinking water. Economicand technological limitations have stymied the advance of ultrasoundtechnology into the realm of industrial scale processes. Ultrasonictransducers are either piezoelectric or magnetostrictive devices.

There is mounting evidence that stressors, such as abrasions or physicaldamage incurred during disinfection, augment the disinfection process.The combination of technologies proposed here utilizes the disinfectionpower of ozone coupled with an acoustic transducer. This device has beendemonstrated to increase the mass transport rate of ozone into solutionand promote energetic inter-particle collisions that lead to particlesize reduction.

Low-frequency acoustic energy has been evaluated as a control measurefor zebra mussels. An intensity of 195 dB re 1 μPa (corresponding to 4kPa) at frequencies from 36 Hz to 1 kHz had no effect on the vitality ofjuvenile and adult colonies of the zebra mussels. Parallel studies withnon-target species, which included algae (Anabena, Gomphosphaeria,Microcystis, and Apharnisornenon) and zooplankton (Daphnia andLeptodiapiomas), indicated that these species were not adverselyaffected by sound intensity of that magnitude.

The intensity of sound in the acoustic mixer (e.g., an Advanced Sonics™acoustic mixer) is 215 dB re 1 μPa (corresponding to 50 kPa), over anorder of magnitude greater pressure. The organisms are subjected to thesound pressure and hydrodynamic shear forces, the magnitude of which canbe enhanced by the design of the contactor. Simultaneously, ozonebubbles introduced into the contactor are shattered into smaller bubblesby the acoustic field and energetically transported in complextrajectories by acoustic streaming. The nature of the hydrodynamic flowregimes induced by the agitation is a non-linear mixture of effectscaused by cavitation and acoustic streaming. Both “microscaleturbulence” and a larger-scale circulating bulk flow pattern arediscernable. The large-scale flow regime is in part the result of the“mutational” vibrational mode of the transducer imparting momentum tothe fluid in the manner of a rotating cylinder. This larger scale regimeis broken up in the contactor by acoustic focusing projections, whichbehave as baffles at that scale. Thus, the energy dissipation into thefluid is intense. In effect, one is substituting mechanical energy forsome of the chemical energy necessary to inactivate the organisms.

To provide adequate contact residuals for inactivation, ozone must besupplied at a rate greater than the matrix ozone demand consumptionrate. To some degree, this effect can be offset by the nature of theozone contacting system because part of the mechanism of ozonedisinfection appears to be related to the actual contact of anozone-containing gas bubble with the organism rather than to theconcentration of dissolved ozone. A large part of the improvement overthe traditional ozone technology offered in this proposal is in thedegree of contact of ozone bubbles with organisms suspended in thewater.

The Acoustic Process for Onboard Ballast Water Treatment:

The development of an ozone-based treatment system for ballast wateraround the energetic contacting ability of the sonic reactor compressesthe “time-space” requirement for ozone deactivation into a volumecompatible with the current shipping design and also lowers the amountof ozone required to inactivate organisms. If the treatment is conductedduring ballasting, about 5000 gallons per minute may be treated,providing an equivalent ozone contact time of several mg/L residualozone for several minutes. This is typically enough to deactivate thecysts and spores of plankton and microorganisms even in conventionalcircumstances. A block diagram of the process is shown in FIG. 6. Duringballasting, water is pumped (step 24) through a filter or cyclone thatremoves (step 26) particles larger than about 100 μm. The filtered waterenters (step 28) an Advanced Sonics™ contactor along with a 4% ozonestream fed (step 30) by an air compressor 32 supplying −60° C. dewpointair. An additional block indicates residence time (step 34), which maybe a passive residence time in a pipe or an active residence time inanother sonic contactor. Two contactors in series with the treatmentwater and the ozone flowing counter current is one configuration.

The concentration of ozone provided is that which is necessary forlethally contacting a wide spectrum of organisms; that concentration canreadily be determined for various water samples from field testing themodule; the system controls can be programmed to deliver the correctdose of ozone, even in the face of changing demand. Response of thesystem to changing ozone demand can be accomplished by adjusting theincoming flow of water (e.g., reducing the rate at which the water isflushed from the ballast through the contactor) or changing the outputof the ozone generator (e.g., generating more ozone).

The physical configuration of the test module is similar to the diagramin FIG. 7. The unit is skid mounted in a vented acoustic enclosure andvibration-isolated from its environment. A plurality of Advanced Sonics™contactors 36, each 2 feet (0.6 m) in diameter and 8 feet (2.4 m) inheight, are housed in the enclosure, allowing four in operation and twoin reserve. Ballast water is distributively fed into a ballast waterinlet 37 in each of the contactors 36 via an inlet pipe 38, though theballast water first passes through a screen filter 39 to filter outlarger organisms and other objects from the ballast water stream. Ozoneis also fed through ozone inlets 40 into the contactors 36, the ozonebeing supplied from an ozone generator 42, which in turn is fed dried,compressed air through pipe 44. Ballast water exits the contactors 36through a ballast water outlet 46. The ballast water can then be passedthrough a process-byproduct neutralization tank 54, which is coupledwith a reactant supply tank 56. In an operating system, the reactantsupply tank can be replaced with a system for measuring bromide andbromate concentrations and for reducing ozone supply if thoseconcentrations are too high. The resonating member 18 in each contactor36 is controlled by an electronic computer controller 48, which sendscommands to the ozone generator 42 to control sonication in thecontactors 36. The ozone generator 42 can also be provided with acomputerized controller. The contactors 36 are mounted on aspring-loaded platform 48 to isolate the contactors 36 so as to minimizetransfer of vibrations therefrom to the rest of the ship.

The ozone dose required to kill organisms can be lowered by theefficiency of the acoustic contactor. The generator is water-cooled.Additional contact time, if necessary, can be provided downstream in apipe reactor. Dosing and safety operation can be controlled by a logiccontroller using fuzzy logic. Safety is a primary criterion in design,especially since the device will be operated in a confined space. Theentire unit is housed in an 8-foot-by-8-foot shipping container 50,which can be designed to provide acoustic isolation, and which isactively vented outside. Process off gas is vented through an ozonedestruct unit 52, and ozone concentration monitors are placed around theunit and interfaced to interrupts, which can shut down the system.

Ozone concentration and sonic intensity are major variables. Temperaturecan be held constant at 15° C. The ozone concentration in the water canrange from 0.25 to 5.0 mg/L, and the sonic intensity can range from 205to 215 dB re 1 μPa. Ozone concentrations are levels that are maintainedduring the contact period. pH is an additional variable, and it canaffect the bromite/hypobromite chemistry issue.

Reducing Aquatic Invasion Species:

Filtering is used to remove organisms and organic matter that needlesslyconsume disinfectant (ozone, hydrogen peroxide, biocides, etc.), orinterferes in the disinfection processes, such as causing turbidity thatshadows organisms from UV radiation. Finer filtering results inhigher-efficiency disinfection processes. However, as the filteringbecomes finer, so do the system operational problems. Finer filtermeshes are quickly blinded by organisms, organic materials and inorganicmaterials, such as sand or silt. Hydraulic backflushing of the permeateflux is required to clear the filters, which increases the pumpingsystem pressure requirements and increases the pumping horsepower andflow rates needed to meet the high flux rates needed to meet practicalballast water flow requirements. The tradeoff in system cost is drivenby the relationship between fine filtration and the effectiveness of thedisinfectant demand needed to deactivate organisms that are not filteredout, but reside in the permeate. One embodiment employs filtration downto 180 microns utilizing a self-cleaning wedgewire strainer to conditionthe ballast water prior to treatment with ozone.

A commonly used indicator life form for disinfection testing is Bacillussubtilis because of its resistant endospore. Endospores of thisbacterium can be used to assess the efficacy of ozone dosing. B.subtilis var. niger endospores ATCC 9372 are employed as sterilizationindicators for hospitals, food processing, etc. These endospores arecommercially available from SGM Biotech, Inc., in Bozeman, Mont. in anydesired concentration. Vials were obtained with 6.9×10⁷ CFU/0.1 mL inalcohol. When the entire contents of a vial were transferred to a 35 Lvolume, a starting concentration of 1.7×10⁵ CFU/mL (5.24∀0.5 log) wasobtained.

EXPERIMENTAL

Experiments were conducted as batch challenges. Over the course of theozone exposure, samples were collected into sterile polyethylenebottles. Some samples were immediately quenched in sodium thiosulfate tostop any lingering disinfection reactions. It was first verified thatthe sodium thiosulfate did not reduce spore viability by itself.

In the samples, the remaining spore viability was determined byculturing dilutions of the original samples on tryptic soy agar andcounting the colonies that formed. Microscopic examination of some ofthe samples using fluorescence staining techniques that coulddifferentiate between live and deactivated spores was used to confirmthe results of the plate counting techniques. The microscopicexamination used LIVE/DEAD BacLight Viability stains coupled withFluorescence Microscopy (Molecular Probes, Inc., Eugene Oreg.). Theseanalyses were conducted by Dr. Grant Mitman of the Biology DepartmentMontana Tech of the University of Montana.

The overall campaign included the following stages:

-   -   Characterization of the ozone concentration time (“ozone        concentration time” is the integral of ozone concentration over        time) behavior of the surrogate in a simple chemical matrix,        i.e., deionized water at a buffered pH;    -   Characterization of the ozone concentration time behavior of the        surrogate in a synthetic sea water matrix;    -   Using the surrogate to estimate the required ozone dose in an        actual ballast water; and    -   Verification of disinfection of actual ballast water.

A 316 stainless-steel reactor with a capacity of 35 liters was used toconduct all of the experiments. A conical tank was used to prepare eachbatch for testing by the addition of buffer and spores. When syntheticseawater was used, it was mixed in a 750-liter reservoir and deliveredto the 35-liter batch tank for the addition of endospores. The batch wasthen pumped to the reactor. Ozone for the system was generated by anOzonia Model CFS-1A corona discharge system, which was fed on oxygen.The output of the generator was controlled by a Love Controls Series2600 PID controller, which received a 4-20 mA output from an ATIdissolved ozone sensor. Because of the acoustic waves inside thecontactor, the ozone sensor was mounted in an outside recirculation loopwhere it was isolated from the pressure fluctuations. The sensor wascalibrated in the exact configuration it occupied during the testing.The sensor operates in two ranges: 0-20 ppm or 0-2 ppm ozone, and bothof these were calibrated independently. Ozone produced by the generatorwas fed into the contactor through a pair of alundum diffusers locatedat the bottom of the reactor. Ozone escaping the vessel was ventedthrough an ozone destruct unit prior to venting outside. Acousticradiation by the sonic member located in the center of the contactor wasmeasured by a hydrophone. A solenoid-operated sampling valve allowedsamples of the spore suspension to be collected over time.

A record of each experiment was collected by capturing the output of thesensors to a data acquisition system run under HPVee software.

The signals captured were:

-   -   Ozone concentration;    -   Temperature;    -   Power output of ozone generator;    -   Solenoid valve activation during sampling event; and    -   Elapsed time.

The acoustic signals were captured on a Tektronix TDS 210 oscilloscope.The acoustic energy was produced by a 2-inch diameter 4130 steel barsheathed in a CPVC protective cover, driven by a sonic oscillator. Thesystem was brought into resonance by adjusting the rotational speed ofthe drive motor with a variable-frequency controller.

The pH was measured before and after the challenge with an Orion 7 3000pH meter. Both the buffer and spores were added to the 35-liter batchand the tank was agitated for 5 minutes after each addition. The batchwas then transferred to the test reactor for the challenge. Depending onthe type of experiment, sterilized bottles with or without thiosulfatequench solution already present were used to collect samples. Theprocedure for beginning each experiment was to start the sonic agitatorto insure complete dispersal of spores. In experiments where sonicenergy was to be absent, the bar was turned off after 30 seconds ofmixing. The initial sample was collected and the data acquisition systemprogram was initiated. The ozone generator was started, and the samplingvalve was simultaneously bumped to signal the data acquisition systemthat the generator was energized. This time signal essentially definedthe time, 0, of each experiment. A local timer was also started to guidethe sampler in obtaining the time series sample. A purge was made of thedelivery pipe by collecting a small volume of reactor fluid in a beakerand then the actual sample was delivered into the appropriate sterilebottle. The bottle was immediately shaken to distribute the quenchfluid. Even though the sampler may have varied slightly from the exactschedule time of sampling, the real elapsed time could be derived fromthe logged data from operating the sample valve.

The laboratory was equipped with a Nuaire laminar flow hood, a FormaScientific incubator, a Market Forge sterilizer, and a Bio-technologiescolony counter. The procedure for counting viable spores was a directadaptation of the SGM Biotech and standard plate count techniquesprocedure. Dilutions were made in standard EPA water and wastewaterphosphate buffered sterile water. Dilutions of 10¹, 10², 10³ were madein triplicate for each sample. Accordingly, for a typical experimentwhere 6 samples were collected, 54 plates would be inoculated. Theplates were pre-poured with tryptic soy agar, and a 1-mL aliquot of eachdilution was pipetted onto a plate and evenly spread across the surface.

The plates were incubated at 3-35° C. before counting. Three additionalcontrol plates were inoculated with deionized filtered water. Countedcolonies have a black dot in the center from the tallying pen. Thecolonies without the dot remain to be counted. Individual endospores inthe population at the time of sampling are colony forming units (CFU).

The plate counts were periodically verified by filtering the samplesonto a grid and staining with a fluorescent dye. All materials that hadbeen contacted with spores, including vials, dilution bottles, pipettetips, and agar plates were autoclaved at 120° C. for 30 minutes prior todisposal.

Experimental Results:

The Effect of Acoustic Energy on Endospore Viability:

Acoustic energy was evaluated at two intensities for its ability toinduce endospore damage in the absence of ozone. The transducer wasoperated at intensities 205 and 215 dB re 1 μPa in separate experimentsof 60 minutes duration at 75 Hz. Samples of the water were taken every10 minutes over the hour. The results are plotted in FIG. 8 as the logof the number of colony forming units per mL present in the sample.Sonic energy alone does not appear to compromise the viability of theendospores, even after one-hour exposure. Prior work on higher organismshas shown that intensities of 190 dB of sound energy at similarly lowfrequency did no damage. One would expect that the damage would bemediated by cavitation phenomena, such as liquid jetting. The energydensity (watts per volume) at low frequencies is not great enough toinduce the amount of cavitational bubble collapse per unit volumerequired to produce a measurable decline in spore viability.

The Effect of Ozone on Endospore Viability in the Absence of AcousticEnergy:

Ozone is typically delivered to a liquid in a bubble column or with ajet mixer. For the non-acoustic studies, a diffuser array was used whichbroke the ozone stream into a cloud of fine bubbles. These bubbles rosethrough the column of liquid, transferring ozone into the liquid. Aseries of experiments were conducted in which the ozone generator wasfed back the dissolved ozone concentration, as registered by the probe.The concentration was maintained at a specific setpoint level. A typicaldata acquisition plot from these experiments is provided in FIG. 9. Theozone setpoint concentration was 1.5 mg/L, which it approximatelyreaches between 2 and 3 minutes. The plot that drops from left to rightin the chart is the log of colony forming units per mL, which drops fromabout 5 (at 0 minutes) to about 2 (at 5 minutes). The vertical strikesat the bottom indicate when the sampling valve was actuated. The ozone(concentration-time) value for the reduction in viable endospores can becharacterized in the following equation:

$\begin{matrix}{{E = {\int_{0}^{1}{{c(t)}\ {\mathbb{d}t}}}},} & (8)\end{matrix}$where E is the exposure, t is the elapsed time to a sample, and c(t) isthe time-dependent ozone concentration curve. The curves were integratednumerically after the captured data was imported into a spreadsheet. Asimple trapezoidal algorithm was used to perform the integration. Theresults for the ozone-only experiments are shown in FIG. 10. The log 3ozone concentration time value was obtained by regressing the log CFUvs. E for the steeply dipping portion of the curve. The value of Ecorresponding to a log 3 reduction (i.e., about log 2 CFU) wascalculated. All data points follow the same exposure curve, regardlessof the setpoint concentration. Regression of all data over the intervalyield an ozone concentration time of 4.46. The data also indicate that aresistant fraction of the endospore population does not further respondon this time scale with just diffused ozone.The Effect of Acoustic Energy Combined with Ozone on EndosporeViability:

Adopting the same approach as above, acoustic energy at 205 and 215 dBre 1 μPa at 75 Hz was supplied along with the ozone over the same rangeof concentration. The acoustic pressure signal of the sonic devices wasdetected with a hydrophone sensor placed in the reactor. A typical 214dB signal is shown in the captured trace in FIG. 11. In this series ofexperiments with a constant 1.5 mg/L concentration, the applied power ofthe ozone generator was constant; i.e., it was not controlled by thefeedback of the dissolved ozone concentration controller. Higherintensity of applied acoustic energy appears to correlate to an increasein ozone mass transport. Utilizing the slopes of the ozone concentrationcurves, one can calculate an apparent mass transfer coefficient about40% greater for the high acoustic intensity than for the low acousticintensity, which was nominally the same as the sparger. This effect hasbeen noted in other applications of ozone mixing, specifically in theoxidative treatment of waste streams. Intensity of this magnitudecorresponds to pressure fluctuations of over 8 psi.

The bubble dynamics in the 215 dB environment were much more energeticthan at 205 dB intensity. The corresponding pressure wave effects onmixing and mass transport should be evident. These acoustic pressurewaves affect the bubbles by causing them to oscillate about anequilibrium or resonant diameter. The effect of the acoustic energy onozone disinfection is seen in FIGS. 12 (at 205 dB) and 13 (at 215 dB).The log 3 ozone concentration time value decreased from 4.5 to 4.0, andthe number of resistant spores surviving the contact was lower for theacoustically assisted ozonation as the intensity is increased to 215 dB.In the presence of small ozone demand, acoustic energy enhanced ozonedisinfection. The levels of dissolved ozone indicated that an ozoneconcentration time value of about 4 was required to lower the populationof viable B. subtilis endospores by 99.9% in buffered water (pH 7.8)with no additional ozone demand than the spores themselves.

Moving to a matrix closer to actual ballast water, a synthetic seawatermatrix was created according to a standard recipe. The composition ofthe constituent salts is given in Table 1.

TABLE 1 Composition of synthetic seawater: Component Conc. (mg/L) NaF 3SrCl₂.6H₂O 20 H₃BO₃ 30 KBr 100 KCl 700 CaCl₂.2H₂O 1470 Na₂SO₄ 4000MgCl₂.6H₂O 10780 NaCl 23500 Na₂SiO₃.9H₂O 20 Na₄EDTA 1 NaHCO₃ 200

Challenges in this matrix were conducted via a procedure similar to theabove-described deionized water experiments, with acoustic energyapplied, as above, at 75 Hz. The initial ozone delivery rate was thesame as that employed in the 1.5 mg/L setpoint experiment. At thisoutput power (110 watts) at 0.8 m³ hr⁻¹, no measurable dissolved ozoneconcentration was obtained. The amount of disinfectant produced wasmeasured in solution as total chlorine residual. Because ozone isshort-lived, disinfectant dose is expressed as a chlorine residual, agross indicator of oxidative disinfection power. The pH has a markedeffect on disinfection. FIGS. 14 and 15 show the reduction in endosporeviability as a function of initial disinfectant dose (as mg/L chlorine)for pH 7.5 (FIG. 14) and pH 9.2 (FIG. 15). At pH values above 8, asignificant amount of ozone decays to the reactive hydroxyl radicalspecie. The residual disinfection power resulting from the reactions ofozone with bromide and other species, such as ammonia, is much greater,lasting for up to two days.

The ozone concentration time value for endospore deactivation is farsmaller than for the bromine species resulting from ozone oxidation ofbromide. For disinfection applications in waters of high demands, thecontactor technology is capable of pumping ozone into the liquid at arate sufficient to maintain a metastable steady state concentration ofdissolved ozone above the required threshold for rapid deactivation ofspores. The contactor has the following two characteristics that lendthemselves to operation in this manner: 1) superior gas/liquid masstransport characteristics; and 2) vigorous bubble dynamics that improvecontact of the bubbles with suspended life forms.

The shortened contact time at high dissolved-ozone concentration enablesthe holding and contact vessels to be sized in a reasonably smallvolume, but compatible with high throughputs of ballast water. Thismetastable ozone concentration need only be maintained for a minute ortwo to obtain the required killing and deactivation. The engineeringdetails of such an approach would be part of the focus of this proposal.For example, the pumping of ozone into the liquid could be staged; i.e.,the acoustic contactor could raise the concentration of ozone to a levelabove the threshold, after which the ballast water would be pumped to aholding tank where the ozone would decay under quiescent conditions. Asecond pulse of ozone could be delivered in a second acoustic contactorafter the first ozone concentration decayed.

Challenge experiments were conducted using synthetic seawater atozone-generator power settings of 440 watts and 660 watts and at gasflow rates of 0.4 and 0.8 m³hr⁻¹. For each power setting, the mass ofozone produced per unit time is independent of the gas flow, to a firstapproximation. A higher gas flow means more bubbles with a lower ozoneconcentration but higher interfacial area, while a low gas flow meansfewer bubbles with a higher concentration but less interfacial area. Athigher power settings (e.g. at 660 watts), a greater amount of gas(i.e., more bubbles or greater interfacial surface area) appears to havea greater effect in promoting the disinfection process than does theproduction of a higher concentration of ozone in fewer bubbles. Theenhanced mass transport of ozone into the liquid results in elevatedconcentrations of oxidation byproducts, which is reflected in residualchlorine measurements.

The basic approach was evaluated with batch challenging of actualballast water. The water came from the hold of a ship originating fromPort Moin, Costa Rica. Ballast water in the ship was sampled in the Portof Philadelphia, and the biota in the samples was characterized by theBigelow Laboratory for Ocean Sciences. About 80% of the water was takenon or exchanged in the Caribbean, while it is believed that theremaining 20% came from the port of origin. The water had been in theballast tanks for 21 days, and total ballast capacity of the vessel was265 cubic meters. The samples were drawn at the 73 cubic meter level.

Results of the chemical analysis showed that the ballast water was notcompletely marine in character. The bromide concentration was 29.2 mg/L,less than half of the typical seawater concentration of 65 mg/L. The pHof the water was near 7.6, while the average ocean water has pH nearer8.2. The chloride concentration in the ballast water was 1.27×10⁴ mg/L.The results of the chemical characterization are shown in Table 2.

TABLE 2 Chemical composition of ballast water. Conc. Conc. Componentmg/L Component mg/L Ca²⁺ 267 Cl⁻ 12700 Mg²⁺ 786 SO₄ ²⁻ 1770 Sr²⁺ 4.9CaCO₃ 9.1 Fe²⁺ 0.5 Br⁻ 29.2 Na⁺ 6130 F⁻ 0.66 K⁺ 248 Mn²⁺ <0.04 pH 7.6 B1.3 TOC <6 Si <0.7 COD na

The characterization of the life forms in each of the eight barrels isgiven in Table 3.

TABLE 3 Summary of biota composition of ballast water obtained fortesting: Barrel Ciliates Dinoflagellates Nematodes Rotifer 1 presentpresent present present 2 present present present 3 present present 4present present 5 present 6 7 present present 8 present present

An initial challenge of the ballast water was made using Barrel #4 whichcontained a variety of organisms. B. subtilis endospores were added toassess the degree of disinfection occurring. Testing was conducted atozone generator power settings from 110 to 440 watts with gas flows of0.4 and 0.8 m³ hr⁻¹. A typical trace of ozone concentration (mg/L) as afunction of time for a power of 440 watts and 0.8 m³ hr⁻¹ is shown inFIG. 16. As is seen in FIG. 17 (where the upper-most plot at 3, 4 and 5minutes is for the 100 watt sample), the 440-watt power setting was mosteffective for disinfection. The 0.8 m³ hr⁻¹ flow was slightly faster inachieving a given level of spore deactivation. However, the level ofdissolved ozone for either condition was not significantly different,but the chlorine equivalent concentration in the high gas flow wasnearly double that of the low gas flow.

A challenge was made of unfortified ballast water (without B. subtilisendospores) to assess the killing of organisms contained in the ballastwater. For this test, an applied ozone power of 660 watts was used with0.8 m³hr⁻¹. The samples were quenched by adding 10 ml of 1% sodiumthiosulfate to the 1 L HDPE collection bottles prior to collecting thesamples. A control sample without ozone treatment or quenchant wassubmitted along with a control containing the quenchant withouttreatment. Observations from Bigelow Laboratories indicate that thesodium thiosulfate did not adversely affect the organisms in thesamples, as the controls were both similar to the originalcharacterization samples submitted earlier.

The treatment times for the samples were in one-minute increments fromone to five minutes. Analysis of the treated samples by BigelowLaboratories (see tables, below) showed that the samples were nearlydevoid of life. Even though all treated samples were positive forbacteria and zooflagellates, there were no ciliates, dinoflagellates,nematodes, etc., observed. Of the thirty culture media tests for thetreated samples, only the one-minute treated sample showed positivegrowth of a green coccoid alga in the DYU medium. Accordingly, and asreported by Bigelow Laboratories, the treatment process drasticallyreduced the numbers and kinds of living organisms.

Phase II Testing at Higher Frequencies in a Flowing System:

Samples 1A-6A:

A summary of data from harbor water samples that were examined byBigelow Laboratory is provided in Table 4, below. Bigelow Laboratoryinoculated 200 μL of sample into various media the day after the sampleswere collected. The flow rate, water pressure (PSI), temperature,ultrasonic treatment system (UTS) and ozone treatment values wereprovided by ETI. The hydrogen ion concentration (pH) and salinity valueswere determined at Bigelow Laboratory. Culture treatments included testsfor the presence of bacteria and fungi [peptonemethylamine broth (PM),peptone broth (P), test medium (TM), malt broth (M)] and tests for thepresence of phytoplankton [DY-V medium, freshwater (DYV), K medium,oceanic (K), L1+NH₄, coastal (L1+NH₄), black sea medium, brackish at 16psu (Blk Sea), L1/24 medium, coastal at 24 psu (L1/24), Prov medium,coastal enriched with soil extract (Prov)]. Bacterial growth (Bac)developed in all of the bacterial test media. Phytoplankton (PHY) grewin all algal growth media (see footnotes for details).

TABLE 4 Flow Temp Sample Location Rate (° F.) UTS Ozone pH Salinity PM PTM M DYV K L1 + NH₄ Blk Sea L1/24 Prov 1A Inlet 125 gpm 74 Full¹ Full²7.0 8 psu Bac Bac Bac Bac PHY³ PHY⁴ PHY⁵ PHY⁶ PHY⁷ PHY⁸ 2A Inlet 125 gpm74 Full¹ Full² 7.0 8 psu Bac Bac Bac Bac PHY³ PHY⁴ PHY⁵ PHY⁶ PHY⁷ PHY⁸3A Outlet 125 gpm 75 Full¹ Full² 7.0 8 psu Bac Bac Bac Bac PHY³ PHY⁴PHY⁵ PHY⁶ PHY⁷ PHY⁸ 4A Outlet 125 gpm 75 Full¹ Full² 7.0 8 psu Bac BacBac Bac PHY³ PHY⁴ PHY⁵ PHY⁶ PHY⁷ PHY⁸ 5A Strainer 125 gpm 74 Full¹ Full²7.1 8 psu Bac Bac Bac Bac PHY³ PHY⁴ PHY⁵ PHY⁶ PHY⁷ PHY⁸ 6A Strainer 125gpm 74 Full¹ Full² 7.1 8 psu Bac Bac Bac Bac PHY³ PHY⁴ PHY⁵ PHY⁶ PHY⁷PHY⁸ ¹In this table, and in each of the following tables, “Full” UTS is20,000 watts at dual frequencies of 16 and 20 kHz. ²In this table, andin each of the following tables, “Full” ozone is a concentration of 1.0mg/L in the ballast water. ³Various diatoms, especially Thalassiosira,zooflagellates (e.g., Cafeteria). ⁴Predominately diatoms (e.g.,Skeletonema, Chaetoceros, Thalassiosira) and zooflagellates (e.g.,Cafeteria). ⁵Predominately diatoms (e.g., Cylindrotheca, Thalassiosira,Skeletonema Chaetoceros). ⁶Predominately diatoms (e.g., Cylindrotheca,Thalassiosira, Skeletonema Chaetoceros) and zooflagellates (e.g.,Cafeteria). ⁷Diatoms (e.g., Thalassiosira, Skeletonema), cryptophtes(probably Rhodomonas and/or Proteomonas) and zooflagellates.⁸Predominately zooflagellates (e.g., Cafeteria), some Thalassiosira,Chaetoceros.Samples 7A-15A:

Table 5, below, provides a summary of data from a second batch of harborwater samples that were likewise examined by Bigelow Laboratory the dayafter they were collected. 200 μL of sample was inoculated into variousmedia. The flow rate, water pressure (PSI), temperature, ultrasonictreatment system (UTS) and ozone treatment values were provided by ETI.The hydrogen ion concentration (pH) and salinity values were determinedat Bigelow Laboratory. Culture treatments included tests for thepresence of bacteria and fungi [peptonemethylamine broth (PM), peptonebroth (P), test medium (TM), malt broth (M)] and tests for the presenceof phytoplankton [DY-V medium, freshwater (DYV), K medium, oceanic (K),L1+NH₄, coastal (L1+NH₄), black sea medium, brackish at 16 psu (BlkSea), L1/24 medium, coastal at 24 psu (L1/24), Prov medium, coastalenriched with soil extract (Prov)]. Bacterial growth (Bac) developed inall of the bacterial test media. Phytoplankton (PHY) grew in all algalgrowth media (see footnotes for details).

TABLE 5 Temp Sample Location Flow Rate (° F.) UTS Ozone pH Salinity PM PTM M DYV K L1 + NH4 Blk Sea L1/24 Prov  7A Inlet 30 gpm 60 Full Off 7.0 10 psu Bac Bac Bac Bac PHY¹ PHY² PHY³ PHY⁴ PHY⁵ PHY⁶  8A Outlet 30 gpm60 Full Off 7.0 9.5 psu Bac Bac Bac Bac PHY¹ PHY² PHY³ PHY⁴ PHY⁴ PHY⁶ 9A Strainer 30 gpm 66 Full Off 7.0 9.5 psu Bac Bac Bac Bac PHY¹ PHY²PHY³ PHY⁴ PHY⁴ PHY⁶ 10A Inlet 10 gpm 66 Full Off 7.0  10 psu Bac Bac BacBac PHY¹ PHY² PHY³ PHY⁴ PHY⁴ PHY⁶ 11A Outlet 10 gpm 66 Full Off 7.0 9.5psu Bac Bac Bac Bac PHY¹ PHY² PHY³ PHY⁴ PHY⁴ PHY⁶ 12A Strainer 10 gpm 66Full Off 7.0 9.5 psu Bac Bac Bac Bac PHY¹ PHY² PHY³ PHY⁴ PHY⁴ PHY⁶ 13AInlet 50 gpm 66 Full Off 7.0  10 psu Bac Bac Bac Bac PHY¹ PHY² PHY³ PHY⁴PHY⁴ PHY⁶ 14A Outlet 50 gpm 66 Full Off 7.0 9.5 psu Bac Bac Bac Bac PHY¹PHY² PHY³ PHY⁴ PHY⁴ PHY⁶ 15A Strainer 50 gpm 66 Full Off 7.0 9.5 psu BacBac Bac Bac PHY¹ PHY² PHY³ PHY⁴ PHY⁴ PHY⁶ ¹Predominately zooflagellates(e.g., Cafeteria and Paraphysomonas). ²Predominately zooflagellates(e.g., Cafeteria), some Thalassiosira, Skeletonema and ciliates.³Predominately zooflagellates (e.g., Cafeteria) some Ochromonas andciliates. ⁴Predominately zooflagellates (e.g., Cafeteria) someCoscinodiscus and ciliates. ⁵Predominately zooflagellates (e.g.,Cafeteria) some Skeletonema. ⁶Predominately zooflagellates (e.g.,Cafeteria) some Ochromonas and Skeletonema.Samples 16A-27A:

A summary of data is provided in Table 6, below, from a second batch ofharbor water samples that were likewise examined by Bigelow Laboratorythe day after they were collected. 200 μL of sample was inoculated intovarious media. The flow rate, water pressure (PS), temperature,ultrasonic treatment system (UTS) and ozone treatment values wereprovided by ETI. The hydrogen ion concentration (pH) and salinity valueswere determined at Bigelow Laboratory. Culture treatments included testsfor the presence of bacteria and fungi [peptonemethylamine broth (PM),peptone broth (P), test medium (TM), malt broth (M)] and tests for thepresence of phytoplankton [DY-V medium, freshwater (DYV), K medium,oceanic (K), L1+NH₄, coastal (L1+NH₄), black sea medium, brackish at 16psu (Blk Sea), L1/24 medium, coastal at 24 psu (L1/24), Prov medium,coastal enriched with soil extract (Prov)]. Bacterial growth (Bac)developed in all of the bacterial test media. Zooflagellates (Zoo) grewin all algal growth media from inlet and strainer samples but none fromthe outlet samples.

TABLE 6 Temp Sample Location Flow Rate (° F.) UTS Ozone pH Salinity PM PTM M DYV K L1 + NH₄ Blk Sea L1/24 Prov 16A Inlet 10 gpm 65 Full 60.0%7.1 7 psu Bac Bac Bac Bac Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹ 17A Outlet 10gpm 65 Full 60.0% 7.4 7 psu Bac Bac Bac Bac — — — — — — 18A Strainer 10gpm 65 Full 60.0% 7.1 7 psu Bac Bac Bac Bac Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹Zoo¹ 19A Inlet 30 gpm 65 Full 60.0% 7.1 7 psu Bac Bac Bac Bac Zoo¹ Zoo¹Zoo¹ Zoo¹ Zoo¹ Zoo¹ 20A Outlet 30 gpm 65 Full 60.0% 7.4 7 psu Bac BacBac Bac — — — — — — 21A Strainer 30 gpm 65 Full 60.0% 7.1 7 psu Bac BacBac Bac Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹ 22A Inlet 50 gpm 65 Full 60.0% 7.17 psu Bac Bac Bac Bac Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹ 23A Outlet 50 gpm 65Full 60.0% 7.4 7 psu Bac Bac Bac Bac — — — — — — 24A Strainer 50 gpm 65Full 60.0% 7.1 7 psu Bac Bac Bac Bac Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹ 25AInlet 88 gpm 65 Full 60.0% 7.1 7 psu Bac Bac Bac Bac Zoo¹ Zoo¹ Zoo¹ Zoo¹Zoo¹ Zoo¹ 26A Outlet 88 gpm 65 Full 60.0% 7.2 7 psu Bac Bac Bac Bac — —— — — — 27A Strainer 88 gpm 65 Full 60.0% 7.1 7 psu Bac Bac Bac Bac Zoo¹Zoo¹ Zoo¹ Zoo¹ Zoo¹ Zoo¹ ¹Predominately zooflagellates (e.g.,Cafeteria).Samples 28A-38A:

In table 7, below, a summary of data is provided from a second batch ofharbor water samples that were likewise examined by Bigelow Laboratorythe day after they were collected. 200 μL of sample was inoculated intovarious media. The flow rate, water pressure (PS), temperature,ultrasonic treatment system (UTS) and ozone treatment values wereprovided by ETI. The hydrogen ion concentration (pH) and salinity valueswere determined at Bigelow Laboratory. Culture treatments included testsfor the presence of bacteria and fungi [peptonemethylamine broth (PM),peptone broth (P), test medium (TM), malt broth (M)] and tests for thepresence of phytoplankton [DY-V medium, freshwater (DYV), K medium,oceanic (K), L1+NH₄, coastal (L1+NH₄), black sea medium, brackish at 16psu (Blk Sea), L1/24 medium, coastal at 24 psu (L1/24), Prov medium,coastal enriched with soil extract (Prov)]. Bacterial growth (Bac)developed in all test media without ozone treatment or growth (Bac)developed in all test media without ozone treatment or with a flow rateover 30 gpm.

TABLE 7 Temp Sample Location Flow Rate (° F.) UTS Ozone pH Salinity PMBP TM M DYV K L1 + NH₄ Blk Sea L1/24 Prov 28A Inlet 30 gpm 63 — — 7.1 9psu Bac Bac Bac Bac — — — — — — 29A¹ Outlet 10 gpm 63 Full Full 7.1 9psu — — — — — — — — — — 30A Outlet 10 gpm 63 Off Full 7.1 9 psu — — — —— — — — — — 31A Outlet 10 gpm 63 Full Off 7.1 9 psu Bac — Bac Bac — — —— — — 32A¹ Outlet 30 gpm 63 Full Full 7.1 9 psu — — — — — — — — — — 33AOutlet 30 gpm 63 Off Full 7.1 9 psu — — — — — — — — — — 34A Outlet 30gpm 63 Full Off 7.1 9 psu Bac Bac Bac Bac — — — — — — 35A¹ Outlet 50 gpm63 Full Full 7.1 9 psu Bac² — Bac³ Bac³ — — — — — — 36A Outlet 50 gpm 63Off Full 7.1 9 psu — Bac Bac Bac — — — — — — 37A Outlet 50 gpm 63 FullOff 7.1 9 psu Bac Bac Bac Bac — — — — — — 38A¹ Outlet 100 gpm  63 FullFull 7.1 9 psu Bac Bac Bac Bac — — — — — — ¹Triplicate cultures forbacterial and algal growth; results (presence, absence) were identicalin all three replicates unless otherwise indicated. ²One of thetriplicate cultures had bacteria, the other two tested negative for thepresence of bacteria. ³One of the triplicate cultures had bacteria, theother two tested negative for the presence of bacteria.

In table 8, below, a summary of data is provided from a second batch ofharbor water samples that were likewise examined by Bigelow Laboratorythe day after they were collected. 200 μL of sample was inoculated intovarious media. The flow rate, water pressure (PSI), temperature,ultrasonic treatment system (UTS) and ozone treatment values wereprovided by ETI. The hydrogen ion concentration (pH) and salinity valueswere determined at Bigelow Laboratory. Culture treatments included testsfor the presence of bacteria and fungi [peptonemethylamine broth (PM),peptone broth (P), test medium (TM), malt broth (M)] and tests for thepresence of phytoplankton [DY-V medium, freshwater (DYV), K medium,oceanic (K), L1+NH₄, coastal (L1+NH₄), black sea medium, brackish at 16psu (Blk Sea), L1/24 medium, coastal at 24 psu (L1/24), Prov medium,coastal enriched with soil extract (Prov)]. Bacterial growth (Bac)developed in all of the bacterial test media without ozone treatment.

TABLE 8 Temp Sample Location Flow Rate (° F.) UTS Ozone pH Salinity PM PTM M DYV K L1 + NH₄ Blk Sea L1/24 Prov 40A Inlet 30 gpm 60 — — 7.7 37psu Bac Bac Bac Bac — — — — — — 41A¹ Outlet 30 gpm 60 Full Full 7.9 37psu — — — — — — — — — — 42A Outlet 30 gpm 60 Full Off 7.7 37 psu Bac —Bac Bac — — — — — — 43A Outlet 30 gpm 60 Off Full 7.8 37 psu — — — — — —— — — — 44A¹ Outlet 10 gpm 60 Full Full 7.9 37 psu — — — — — — — — — —45A Outlet 10 gpm 60 Full Off 7.7 37 psu Bac — Bac Bac — — — — — — 46AOutlet 10 gpm 60 Off Full 7.8 37 psu — — — — — — — — — — ¹Triplicatecultures for bacterial and algal growth; results (presence, absence)were identical in all three replicates.

The above tables show that outlet samples, after receiving full ozonetreatment at flow rates of 30 gpm or less, contained no livingmicroorganisms that were present in the ballast inlet samples.Accordingly, these treatments killed all bacteria, as evidenced by nobacterial growth in the samples after a 21-day incubation.

The following tables report data generated at the University ofMaryland-Baltimore County, measuring the amount of bromide and bromatein water including dissolved ozone. “Bay water” samples were taken fromthe inner harbor in Baltimore, Md. The “ballast water” samples weretaken from deep sea on board the ship, Cape Wrath, at latitude 30°21.8′N and longitude 34° 03.8′W. The results show that bromides andbromates are not generated in substantial amounts in water treated atthe flow rates that were shown, above, to offer effective kill rates inthe ballast water samples. The natural amount of bromide found incoastal waters is 65 mg/L, and the treated samples did not varysubstantially from this norm.

TABLE 9 Conc. of Conc. of Flow Rate Conductivity Bromide Bromate SampleID Outlet/Inlet (GPM pH@ 24° C. @ 24° C. (mS) Ozone (ppm) % RSD (ppm) %RSD Bay Water Inlet 10-20-50-88 7.54 10.45 absent 24.93 3.05 0.0049 0.34Bay Water Outlet 10 7.29 10.55 absent 21.98 3.71 0.172 3.15 (2) BayWater Outlet 30 7.43 10.60 absent 23.82 1.11 0.120 2.49 (4) Bay WaterOutlet 50 7.38 10.58 absent 25.23 1.07 0.113 6.03 (6) Bay Water Outlet88 7.50 11.00 absent 24.10 1.72 ND — (8)

TABLE 10 Conductivity Conc. of Conc. of Flow Rate @ 24° C. BromideBromate Sample ID Outlet/Inlet (GPM pH@ 24° C. (mS) Ozone (ppm) % RSD(ppm) % RSD Bay Water Inlet 10-30-50-100 7.25 15.11 absent 30.32 1.97 ND— (12) Bay Water Outlet 10 6.81 15.00 present* 27.11 7.83 0.223 6.47 (9)Bay Water Outlet 30 7.17 15.39 absent 28.20 2.60 0.091 0.29 (10) BayWater Outlet 50 7.19 14.95 absent 30.02 3.33 0.090 0.07 (11) Bay WaterOutlet 100 7.23 15.01 absent 31.70 2.25 ND — (13)

TABLE 11 Conductivity Conc. of Conc. of Flow Rate pH@ @ 24° C. BromideBromate Sample ID Outlet/Inlet (GPM 24° C. (mS) Ozone (ppm) % RSD (ppm)% RSD Ballast Inlet 10-30 7.89 36.6 absent 77.86 0.52 ND — Water (15)Ballast Outlet 10 8.20 40.80 present* 73.65 0.90 0.400 1.18 Water (17)Ballast Outlet 30 8.11 35.20 present* 75.95 0.60 ND — Water (16)

Ozone was present in the range of 0.01 to 0.1 mg/L in the ballast watersamples collected from the outlet and also in one of the bay watersamples collected from the outlet with a very low flow rate.

CONCLUSIONS

The challenge experiments (based on deactivation of B. subtilisendospores) indicate that treatment of ballast water in the soniccontacting device is possible, even in marine brines. Although the sonicdevice does not appear to produce sufficient energy density to damagesmaller particles such as spores or cysts directly, the gas-liquid masstransport aspects of acoustic fields and small scale micromixingfunction to make the technology ideal for agitating a contact vessel forozone treatment of the ballast water.

The ozone should be delivered fast enough that a transient steady stateozone concentration can be maintained between 0.5 and 1 mg/L for severalminutes time. The dosing of ozone required to achieve this conditionwill be strongly a function of the ballast water type, the greatestdemand coming from completely marine waters, as one might suspect. Therewill be an optimum ozone gas concentration and volumetric flow regimethat will minimize the amount of oxidation byproduct formation, butprovide reasonable disinfection. Where this optimum occurs in terms ofoperational parameters will depend on the configuration of the flowthrough contact unit and nature of the bubble dynamics inside thecontractor.

For disinfection to occur rapidly, the creatures must experience anozone concentration, either in the bulk liquid or in the film around thegas bubble. The ozone must be transferred from the bubble at a rate fastenough to keep pace with the many demand reactions, yet still provide asmall steady state ozone concentration. If too much aqueous ozone ispresent at steady state, the rate of some parasitic reactions may beaccelerated. If too little is supplied by the bubble, a concentration ofozone can't be maintained for disinfection. Contact with the bubbles isimportant for disinfection also.

The ResonantSonic™ device can supply ozone quickly enough, enhancingozone transfer through the acoustic bubble pumping and boundary layerdisruption. Bubble contact is promoted through micromixing. Simplypromoting mass transfer of ozone into the liquid alone will not sufficeto optimize the process. The number of bubbles and their ozoneconcentration and the configuration of the bubble introduction into theacoustic field can all be balanced in an effort to achieve optimaldisinfection.

The indications are that the sonic ozone contactor provides means toshorten the contact time for disinfection by creating a metastabledissolved-ozone concentration in ballast water through increasedgas-liquid mass transport during contacting. Thus, dissolved ozoneserves as a process-monitoring variable during the disinfection process.

Fluid dynamic modeling can be employed to optimize chamber design forgas bubble interaction with the acoustic field during the fluidresidence time in the reactor. Consideration is also made for recyclingof ozone-containing gas streams.

Ozone concentration time required by the process is established by theamount of “kill” required for disinfection of the ballast water, whichis determined by a multiple log 10 reduction of the target species,typically by a log 10 of three or four. The experimental work indicatedthat the ozone concentration time was a function of the ozoneconcentration level, the sonication process and exposure of thecontaminated ballast water laden with ozone after the sonic radiationhad been terminated.

During the experimental work, it was observed that the parasitic ozonedemand rate was different with and without sonic radiation, as was theeffectiveness of ozone for disinfection. Disinfection is carried outmost efficiently by using the least amount of ozone and reducing theamount of processing equipment volume, while sustaining sufficientballast water flow to make the overall process practical for use as aballast water disinfection method. Intensified contacting of the ballastwater with sonic energy and high-concentration ozone for a brief periodfollowed by transfer to a quiescent vessel for a contact period can befollowed by a second energetic ozone pulse.

Ozonation of waters containing bromide result in the formation ofbromate. Sea water typically contains 65 ppm bromide, which can beconverted to several tens of ppm bromate. US drinking water, treatmentstandards will probably require that the bromate level be maintainedbelow 1 ppb.

Optimization tests can still utilize B. subtilis as an indicator speciefor contacting efficiency, with the same analytical procedure aspreviously used. As more data become available, the B. subtilis ozoneconcentration time can be related to the necessary exposure for moredifficult forms of nuisance species.

Additional details relating to the apparatus and methods describedherein are provided in U.S. Ser. No. 60/488,358 (filed Jul. 18, 2003)and U.S. Ser. No. 60/536,428 (filed Jan. 14, 2004), both of which areincorporated herein by reference in their entirety.

In describing embodiments of the invention, specific terminology is usedfor the sake of clarity. However, the invention is not limited to thespecific terms so selected, and each specific term at least includes alltechnical and functional equivalents that operate in a similar manner toaccomplish a similar purpose. In addition, it should be understood thatin some instances where a particular embodiment of the inventionincludes a plurality of system elements or method steps, those elementsor steps may be replaced with a single element or step and vice versa.Likewise, while this invention has been shown and described withreferences to particular embodiments thereof, those skilled in the artwill understand that various changes in form and details may be madetherein without departing from the scope of the invention.

1. A method for treating ballast water emitted from a ballast tank of awater-borne ship, the method comprising: allowing water to flow out ofthe ballast tank; passing the water through a cylindrical tank after itflows out of the ballast tank, the passing comprising causing the waterto enter the cylindrical tank through a water inlet and exit thecylindrical tank through a water outlet that are disposed proximate totwo opposite ends of the cylindrical tank; injecting ozone into thewater in the cylindrical tank via an ozone inlet disposed proximate tothe water inlet; supplying acoustic energy into the water as the waterpasses from the water inlet to the water outlet, the acoustic energybeing supplied by an acoustic mixing machine that comprises a mechanicalmember and an oscillator whose rotational frequency is adjusted to bringthe mechanical member into resonance, the mechanical member comprisingone or more of a hollow tube resonator and a solid bar that ispositioned within the cylindrical tank approximately along a centralaxis of the cylindrical tank such that a first end of the mechanicalmember is proximate to the water inlet and a second end of themechanical member is proximate to the water outlet, the mechanicalmember generating acoustic energy that is communicated to the ballastwater contained in the cylindrical tank thereby causing the ballastwater in the cylindrical tank to move through the tank from the waterinlet to the water outlet with a circulating bulk flow pattern; breakingup the circulating bulk flow pattern to dissipate additional energy intothe water, the breaking up occurring as the water encounters one or moreacoustic focusing projections positioned within the cylindrical tank andinto the circulating bulk flow pattern to thereby to dissipateadditional energy into the water; and releasing the ballast water fromthe ship after the water exits the contactor.
 2. The method of claim 1,wherein the acoustic energy is applied at dual frequencies.
 3. Themethod of claim 2, wherein the dual frequencies are both in the range ofabout 16 kHz to 20 kHz.
 4. The method of claim 3, wherein the dualfrequencies are about 16 kHz and about 20 kHz.
 5. The method of claim 1,wherein the acoustic energy is delivered at a power of at least 20,000watts.
 6. The method of claim 1, wherein the contactor apparatus ismounted on board the ship.
 7. The method of claim 1, wherein organismsand other matter having dimensions larger than about 100 μm are removedfrom the ballast water before the ballast water passes through thecontactor.
 8. The method of claim 1, wherein the injected ozone andacoustic energy do not enter the ballast tanks.
 9. The method of claim1, wherein ozone is injected into the ballast water to form aconcentration of ozone in the ballast water between about 0.5 and about1.0 mg/L.
 10. The method of claim 1, further comprising exposing thewater to a quiescent period and then passing the water through thecontactor apparatus again or through a second contactor apparatus. 11.The method of claim 1, further comprising measuring bromide and bromateconcentrations and controlling the injecting of ozone into the contactorbased on the measured bromide and bromate concentrations.
 12. The methodof claim 1, further comprising passing the water to a process-by-productneutralization tank before releasing the ballast water from the ship andadding one or more reagents to destroy bromide and/or bromate compoundsin the process-by-product neutralization tank.
 13. A contactor apparatusfor disinfecting ballast water, the contactor apparatus comprising: acylindrical tank through which the ballast water can flow and whichcomprises a water inlet and a water outlet that are disposed proximateto two opposite ends of the cylindrical tank and an ozone inlet disposedproximate to the water inlet; an acoustic mixing machine that comprisesa mechanical member and an oscillator whose rotational frequency isadjusted to bring the mechanical member into resonance, the mechanicalmember comprising one or more of a hollow tube resonator and a solid barthat is positioned within the cylindrical tank approximately along acentral axis of the cylindrical tank such that a first end of themechanical member is proximate to the water inlet and a second end ofthe mechanical member is proximate to the water outlet, the mechanicalmember generating acoustic energy that is communicated to the ballastwater contained in the cylindrical tank, thereby causing the ballastwater in the cylindrical tank to move through the tank from the waterinlet to the water outlet with a circulating bulk flow pattern; one ormore acoustic focusing projections positioned within the cylindricaltank and into the circulating bulk flow pattern to thereby dissipateadditional energy into the water; and an ozone source coupled with thecontactor for supplying ozone into the cylindrical tank via the ozoneinlet.
 14. The contactor apparatus of claim 13, further comprisingwherein plurality of resonating members within the cylindrical tank. 15.The contactor apparatus of claim 13, further comprising a quiescentcontainer into which the water is passed after the and then passing thewater through the contactor apparatus again or through a secondcontactor apparatus.
 16. The contactor apparatus of claim 13, furthercomprising: a system for measuring bromide and bromate concentrations inthe water, the system providing a feedback signal; and a processor thatcontrols the source of ozone to control a rate at which ozone issupplied to the water contained in the tank, the processor controllingthe rate based on the measured bromide and bromate concentrations. 17.The contactor apparatus of claim 13, wherein the resonating membergenerates acoustic energy at frequencies in the range of about 16 kHz toabout 20 kHz.
 18. A ship suitable for sailing the seas, the shipcomprising: one or more ballast tanks; one or more outlet passagescoupled with ballast tank(s) for discharging ballast water from theballast tanks, the outlet passage(s) having a discharge port fordischarging ballast water from the ship; one or more inlet passagescoupled with ballast tank(s) for supplying water to the ballast tanks,the inlet passage(s) having an intake port for intake of ballast waterfrom outside the ship; and a contactor apparatus coupled with the outletpassage, enabling ballast water to flow out of the ballast tank(s)through the outlet passage(s) and through the contactor apparatus beforeleaving the ship, the contactor apparatus comprising one or more sonicgenerators for generating acoustic energy and a source of ozone, thecontactor apparatus further comprising: a cylindrical tank through whichthe ballast water can flow and which comprises a water inlet and a wateroutlet that are disposed proximate to two opposite ends of thecylindrical tank and an ozone inlet disposed proximate to the waterinlet, the ozone inlet supplying ozone from the source of ozone to theballast water in the cylindrical tank; an acoustic mixing machine thatcomprises a mechanical member and an oscillator whose rotationalfrequency is adjusted to bring the mechanical member into resonance, themechanical member comprising one or more of a hollow tube resonator anda solid bar that is positioned within the cylindrical tank approximatelyalong a central axis of the cylindrical tank such that a first end ofthe mechanical member is proximate to the water inlet and a second endof the mechanical member is proximate to the water outlet the mechanicalmember generating acoustic energy that is communicated to the ballastwater contained in the cylindrical tank, thereby causing the ballastwater in the cylindrical tank to move through the tank from the waterinlet to the water outlet with a circulating bulk flow pattern; and oneor more acoustic focusing projections positioned within the cylindricaltank and into the circulating bulk flow pattern to thereby to dissipateadditional energy into the water.
 19. The ship of claim 18, wherein theinlet port is positioned below the discharge port such that the inletport can be submerged in a body of water while the discharge port isabove the body of water when the ship is in the body of water.
 20. Theship of claim 18, wherein the contactor comprises a plurality ofmechanical members.